Laboratory Manual for Introductory Geology 4e

FIGURE 17.24 Counterclockwise wind circulation in 2017 hurricanes Harvey, Irma, and Maria.
(b) Hurricane Irma approaching Cuba and Florida (September 8,
2017).
(a) Hurricane Harvey filled most of the Gulf of Mexico as it
approached Texas (August 24, 2017).
Most hurricanes are 250 to 300 miles wide, including the
eye, which is typically 20 to 40 miles across. For comparison,
Katrina was 350 miles across, Harvey 250 miles, Irma
300 miles, Maria 200 miles, and “superstorm” Sandy 1,000
miles. Steering currents in the atmosphere push hurricanes
slowly, generally at 10 to 15 miles per hour, although Hurricane
Irma moved inland much faster. Winds throughout
the lower atmosphere, ocean temperature variations, and
interactions with landmasses make it difficult to predict the
path of a hurricane accurately.
When Hurricanes Harvey, Irma, and Maria made landfall
in the Caribbean and on the U.S. mainland, they demonstrated
all too clearly the three ways in which hurricanes
can cause severe damage.
(c) Hurricane Maria over Puerto Rico, approaching Cuba and
Florida (September 20, 2017).
■ Wind: When most people think about hurricanes, they immediately think
about the strong winds associated with them as the greatest danger. But strong winds
are only one of three factors that cause damage during a hurricane and they are not
always the biggest threat. Yet, the danger from hurricane winds is certainly real, especially
from storms such as Irma—the second most powerful hurricane ever recorded,
which maintained a top wind velocity of 185 miles per hour for more than 30
hours. Wind from Irma and Maria devastated several Caribbean islands, including
Puerto Rico and the U.S. Virgin Islands, and destroyed Barbuda (FIG. 17.25). Powerful
winds can flatten trees, blow roofs from houses, and can also turn pieces of debris
into projectiles, shattering windows that might have withstood the wind alone.
■ Storm surge: Winds of 100 to 185 miles per hour are certainly dangerous, but
storm surge, a wall of water driven onshore by a hurricane, can be more hazardous
(FIG. 17.26). Katrina’s storm surge was estimated at 30 feet above normal sea level;
this wall of water carried boats, houses, and other debris far inland, causing widespread
destruction and wiping out entire communities. Irma packed more powerful
winds, but its storm surge reached “only” 8 to 9 feet in Florida.
Why was storm surge from Irma less damaging than that from Katrina or Sandy?
First, the topography of the shoreline can amplify storm surge from a less powerful
storm. Deep embayments, such as New York Harbor, act like a funnel; as storm surge
enters the harbor, it piles up in the narrow end, reaching heights not found on
17.5 WHEN SHORELINES BECOME DANGEROUS
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